WordPress: Custom Media Size Dropdown

functions.php

// Set the new image sizes
if(function_exists( 'add_image_size')){
	add_image_size('blog-large', 900, 700, false);
}

// Tell the media panel to add the new size to the dropbown
function custom_image_sizes($sizes) {
        $addsizes = array(
                "blog-large" => __("X-Large")
                );
        $newsizes = array_merge($sizes, $addsizes);
        return $newsizes;
}
add_filter('image_size_names_choose', 'custom_image_sizes');